Gelcoat Blistering?

[Kalun D]

Having a compatibility issue.

Built fiberglass extensions on the nostril spare tire cover using a styrofoam mold. This was in order to make the nostrils full depth. Made the mistake of not using any gelcoat.

Ready to apply some primer filler but reading directions it says don't use on bare glass. Call the manufacture, says it's because it doesn't adhere properly. So I ask what paint do you have that will adhere so just the bare areas can be sealed. None available from them.

Contact fiberglass supplier, no primer available for direct use on bare glass but you can apply gelcoat on top. So I brush on some gelcoat but it blisters where I've applied some plastic filler. The molded surface was a bit rough so I had already applied some filler. It's too problematic to remove all the filler especially at the blend line. All I can think to do at this point is put a skim coat of plastic filler over the entire area of bare glass.

Any suggestions?

[Scott McDill]

Klaun,
The solvents in the gel coat are melting the filler. The solution is to use an epoxy primer over the fiberglass and filler. The bond is more physical rather than chemical thus requires good sanding prior to application. After it cures it will be inert and resistant to most urethane primers. You will have to sand the epoxy prior to applying the urethane sandable primer to promote a good physical bond. Suggest you stay with the same brand of coatings. The manufacturer will be able to advise further on compatibility and method.

[Jonathan S]

Not all brands of epoxy primer need to be sanded to put a coat over them. I know on PPG you don't need to if you get the next coat on within a certain amount of time. You definitely want to avoid sanding it because it sands poorly. It balls up and clogs your sandpaper.

Whatever you do read the tech sheets for whatever paint or primer you use.

By the way I did exactly what you are talking about and I used epoxy primer over the raw fiberglass with no issues.

[Paul Butvila]

The problem may also be a result of the glass being waxed rather than unwaxed which may be a concern. Sanding first should fix the problem, and a quick wipe down with acetone.

[FRPGUY]

kalun D, I use Duratec 707-060 Gray EZ Sanding Primer. It's a catalized primer and a high build primer. The last gallon I bought cost me $67.00. from Composites One, Bristol, RI. 401-253-4800. This stuff is the best primer you will ever work with and it does sand nice. I use it for making prototypes. Spray right over foam, sand with 220 dry, wet sand 400, 600 and then you can even polish it.

[Kalun D]

I've already purchased the Transtar Euro Classic Primer, at $100 gallon.

It's isocyanate free because I've had trouble in the past.

Going to the paint supply, see what they say about epoxy primers